It has been proposed to provide safety-belts and also air-bags for use in motor vehicles to restrain seat occupants during an accident situation. It is known that if the seat-belt and/or air-bag can prevent a seat occupant from reaching the dashboard or steering wheel in front of the seat during an accident, then the risk of injury to the seat occupant may be minimised.
In any accident situation the energy that has to be absorbed by the seat-belt and/or air-bag to prevent a seat occupant from reaching the dashboard or striking it at high velocity, depends upon a number of different factors including the severity of the accident or, in other words, the degree of deceleration experienced by the cabin of the vehicle, and also the weight of the seat occupant. It is clear that more energy has to be absorbed when the seat is occupied by a heavy person than if the seat is occupied by a light person.
It has been proposed to utilise a force limiter associated with a safety-belt for a seat occupant, the force limiter being controlled by weight sensors located in the seat. The force limiter may have an adjustable force level, so that the energy absorbed by the force limiter may be adjusted. For example, the force limiter may have a force level (or energy-absorption level) that can be changed from a high level to a low level at a controlled moment after commencement of an accident situation.
It has also been proposed to provide an air-bag with controllable venting, so that the energy absorbed by the air-bag may be adjusted.
It is to be understood that a heavy person is capable of withstanding a higher restraint force than a light person. However, it is desired to keep the deceleration force applied to any seat occupant as low as possible or, alternatively, to apply any high force level that needs to be used for as short a time as possible.
It has been found that the weight sensors utilised in presently proposed safety arrangements of the type discussed above are either very expensive, or have other shortcomings.
The present invention seeks to provide an improved safety arrangement.